When designing microelectromechanical systems (MEMS) based devices it is often desirable to have open areas or voids in the structure. Such open areas can be used for thermal isolation, such as making a diaphragm, or for mechanical purposes, such as allowing moving parts. In the current state of the art, such open areas or voids are formed by including solid sacrificial layers within the structure. Once the desired structure is built, the sacrificial layers are chemically dissolved, and the dissolved material is removed to form the open area.
Dissolving starts at the perimeter of the sacrificial layer which is covered by a non-sacrificial layer and works its way in towards the center of the structure. As the sacrificial layer dissolves, the waste products must be removed and fresh etchant must be presented to complete the dissolving processed. A problem however occurs when the MEMS design calls for a very small gap that extends for a relatively long distance (for example, a gap 0.1 micron tall and 200-2000 micron from edge to center). With such an aspect ratio, it becomes difficult to get fresh etchant further into the emerging gap to the sacrificial layer material. At the same time it gets more difficult to get the waste products out. At least in some applications, remaining waste products within the gap can interfere with moving parts. The use of pinholes in non-sacrificial layers that let etchant in and out from the top of the sacrificial layer has been proposed. However, such a solution is also problematic where the function of the gap is to provide a conduit for liquid or gas samples for analysis. Such pinholes would allow outside contaminants to affect the samples, or allow the samples to escape. Similarly, if the gap houses a resonating structure and needs to hold a vacuum, such pinhole can allow outside gasses to enter the gap which will affect the resonating qualities of the structure.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for MEMS device fabrication.